VPD for humidity control

[liquidpower]

Iv been working on this for a few days got it running just wanted to share
flow takes temp and h of grow tent joins them together as an array and sends to the function

Code: Select all

var h = msg.payload[0];
var t = msg.payload[1];

var T = (t- 32) * 5/9 ;
var SVP = (Math.pow(2.71828,(T / (T +238.3) * 17.2694))* 610.78);
//SVP = SVP * 610.78;
var VPD = (((100-h) / 100) * SVP)*10;

VPD = VPD *.001;
msg.topic="vpd"
msg.payload=VPD
return msg;

then i put a switch on the end if its higher then the vpd i want turn humidifier on off once its lower then the number i want.

[LEDG]

Nice! Thanks for sharing! Will definitely give this a try.

Is the first broken image supposed to be the flow?

[Capt. Saicin]

If anyone's interested, this is the code i'm using on arduino. Sourced it from around the web.

Code: Select all

...
VPCanSat = 610.78 * pow (M_E, ((tempCanopy-1.5)/((tempCanopy-1.5)+238.3)*17.2694));
//M_E = euler number
VPAir = VPCanSat * (humAir/100);
VPD = VPCanSat - VPAir;
  ...

TempCanopy is measured in a sensorbox in the canopy. I'm subtracting 1.5°C from that measure to approximate the temperature near the leaf due to cooling while transpiring. HumAir is another sensor in the upper third of the room. I'm not exactly sure if that's wise. I'm a bit unsure whether the VapourPressure in the canopy or upper half is the relevant one here. On the one hand the VP near the canopy is probably relevant for the direct transpirational rate. But the VP in the upper third could act as a "reservoir" to take up moisture...unsure.
What's your take on this?

Happy to be corrected

[ATPinMotion]

Nice work, and good question.

Airspeed should be considered as well. Fans above canopy and/or below?

What is your air exchange rate?

Is supply air coming in low and the exhaust exiting high?

[liquidpower]

first img was a the flow
i'm not looking at air speed or any thing just checking if the temp and humidity put out the ideal VPD goal if humidity is to low per set vpd turn on humidifier.

[LEDG]

Nice thank you

[jaysal]

first img was a the flow
i'm not looking at air speed or any thing just checking if the temp and humidity put out the ideal VPD goal if humidity is to low per set vpd turn on humidifier.

Looks great! Do you mind sharing the Node-RED export for this sequence?

[btbr]

Love a share too if you are able. Little bit stuck trying to get it to work.

[Samsung123]

This is what I'm using in node red to spit out an ideal RH. From there I'm planning to make the ideal humidity into some triggers. Right now I'm just using helpers and adjusting the target manually based of my target VPD.

Code: Select all

function calcRh(targetVpd, tempC) {
    const tempF = tempC * 9/5 + 32
    const rh = 100 * (1 - targetVpd / (3.386 * Math.exp(17.863 - 9621 / (tempF + 460))));
    return rh.toFixed(2);
}

const targetVpd = msg.payload["input_number.target_vpd"]
const tempC = msg.payload["sensor.a_temperature"]

msg.payload = calcRh(targetVpd, tempC)

return msg;